Pythagoras’ daughter-in-law takes off her skirt (by Montaigne and Theanus)

Re-reading the Essays of Michel de Montaigne, I came across the following quotation which he attributed to the daughter-in-law of Pythagoras:

“A woman who sleeps with a man must take off her shame as well as her skirt, and recover it with her petticoats.”

Who could be the “daughter-in-law” of Pythagoras, I wondered? After some googling, I have come to the conclusion that this is a confusion by Montaigne, as several classical authors attribute the quote to Theanus, a prominent Pythagorean who some sources say was Pythagoras’ daughter, others his wife. It is not uncommon to attribute to Theanus the title of “first woman mathematician”, although the above quotation shows that her knowledge and teachings transcended the abstract world of geometry or number theory.